I’ll go out on a limb here and say that FW’s letter is the finest short passage in all of Jane Austen. In just a few sentences, it accomplishes an astonishing amount.

* The letter elegantly solves the plot problem: how to bridge the gap between two rather reticent people who never get to spend more than five minutes alone together.
* It’s entirely convincing as the work of this character (decisive, straight-forward, passionate) under these circumstances (spontaneous outpouring of emotion). It’s choppy, hasty, even (at one point) ungrammatical. Though it is sometimes almost poetic (“Dare not say that man forgets sooner than woman, that his love has an earlier death”), it doesn’t read like a polished piece of rhetoric by a professional writer.
* And yet: how exquisitely JA has structured it! In the first half of the letter, FW evokes, both directly and metaphorically, the pain and loss in his past with Anne. He starts with “You pierce my soul” – a painful, almost violent metaphor – goes on to say that he is “half agony,”and tells her that she nearly broke his heart eight years earlier. He also repeatedly evokes the transient, fragile nature of love – he talks about the possibility that his renewed affection could come too late, that her feelings for him could be gone, that he could have forgotten her, that his love could have died. He admits that he has in some ways failed her: he has been unjust, weak and resentful -- “but never inconstant.”

And just as the fact to which those last three words refer – his constancy – will be the bridge from the pain of the past to the possibility of a new beginning, so too does the phrase provide a bridge from the first half of the letter, with its evocation of the past, to the second half, which is all about the present: “You alone have brought me to Bath. . . .I had not waited even these ten days, could I have read your feelings.” Indeed, we’re quickly not just in the present, but in real time, with FW reporting his emotions and reactions as they occur (“I can hardly write. I am every instant hearing something which overpowers me.” “You sink your voice. . . ” ”You do us justice, indeed.”) And then, as this section of the letter ends, he summarizes her position: “You do believe that there is true attachment and constancy among men.” The alert reader will remember that this phrase – “true attachment and constancy” – is a verbatim echo of Anne’s words a few pages earlier in her conversation with Captain Harville. So in the course of the letter, he moves from a metaphorical evocation of the anguish that she has caused him (“You pierce my soul”) to perfect unison with her – fittingly, on the very phrase that, again, describes the fact that makes this unison possible.
* So, in other words, the movement in the letter recapitulates, in miniature, the arc of the whole narrative – the pain of estrangement healed through the persistence of love. In the letter, FW does not deny or minimize the hurt he and Anne have caused each other – rather, he acknowledges it, moves through it, and arrives at the possibility of reconciliation. Which, I would argue, reflects one of the major themes of Persuasion: that love endures, but that grief and pain have to be acknowledged; that both love and the possibility of its loss – love’s strength and love’s fragility – are equally real.